In manufacturing semiconductor devices such as LSI and super-LSI or in manufacturing a liquid crystal display panel or the like, a circuit pattern is made by irradiating a light to a semiconductor wafer or a negative plate for liquid crystal, but problems occur if a dust particle is sticking to a photographic mask or a reticle (hereinafter these are simply referred to as “photomask”) used in this stage; for then the pattern's edges become blurred and what is more the under base gets smeared in black, whereby the dimension, quality, appearance, and other aspects of the resulting product are degraded.
Thus, these works are usually performed in a clean room, but, even in a clean room, it is yet difficult to keep the photomask clean all the time. Hence, the exposure light irradiation is conducted only after a pattern-bearing part of the surface of the photomask is sheltered by a pellicle as a dust fender. Under such circumstances, foreign particles do not directly adhere to the surface of the photomask, but only onto the pellicle membrane, and thus by setting a photo focus at a pattern on the photomask at the time of lithographing, the foreign particles on the pellicle membrane do not affect the transferred image.
In general, a pellicle is made in a manner such that a transparent pellicle membrane made of cellulose nitrate, cellulose acetate, a fluorine-containing polymer or the like, which transmit light well, is adhered to an upper annular face of a pellicle frame, which is made of an aluminum, a stainless steel, polyethylene or the like, after applying to the upper annular face a solvent which dissolves the pellicle membrane well, and then by drying the solvent by blown air (ref. IP Publication 1), or after applying to the upper annular face an adhesive made of a material such as an acrylic resin or an epoxy resin (ref. IP Publications 2, 3). Further, on a lower annular face of the pellicle frame is laid an agglutinant layer made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicone resin or the like for attaching the pellicle frame to the photomask, and over this agglutinant layer is laid a releasable liner (separator) for protecting the agglutinant layer.
The application of the agglutinant onto the pellicle frame is conducted by brush painting, spraying, dipping, extrusion form a tube or a cartridge, automatic dispensing, or the like (ref. IP Publication 4); however, in any of these procedures, it has been inevitable that a bubble or foam occurs in the agglutinant layer which is thought to originate from the agglutinant itself or from the air trapped between the agglutinant and the pellicle frame as the former is applied to the latter.
Such foam would naturally go out as the agglutinant layer was let to sit for a period; but when the agglutinant is of such a type that it is to be diluted in a solvent, the foam would not go out easily, because as the solvent quickly evaporates, the viscosity of the agglutinant layer increases, making it harder for the foam to penetrate and go out; so that it was necessary to remove the foam as early as possible. For if the foam stays in the agglutinant layer, during a pellicle inspection, it glitters reflecting a focused light beam and is mistaken as foreign particles whereby not only the appearance but also the quality of the agglutinant layer is underestimated and thus the pellicle frame is eliminated off the production line and causes a reduction in the yield of the pellicles manufactured.
A conventional method for removing foam from a liquid has been to use an antifoaming agent. Examples of effective antifoaming agent for non-aqueous foamed liquid include silicone oil-based agents such as KF-96, KS-66, KS-602A, FA-600, FA-630, FL-100, FL-50 (which are commercial products of Shin-Etsu Chemical Co., Ltd.); among these agents fluorine-modified silicone oils such as FA-600, FA-630, FL-100 and FL-50 (which are commercial products of Shin-Etsu Chemical Co., Ltd.) are particularly effective.